With the economic development, power consumption gradually increases, energy consumption significantly grows, and environment problem becomes increasingly prominent, the power plant must use new coal source and develop new burning methods to eliminate the pressure from both energy consumption and environment protection. In recent years, the coal having high base metal content is widely used, which results in hearth slag and heated area ash. Forest waste, agricultural waste, water plant, oil plant, processing wastes of organic matter, human and animal excreta and municipal solid waste are regarded as the regeneration energy with bright application prospect. Compared with common stone coal, the biomass fuel has higher alkali metal content and thus is easily gasified during the burning process, which often results in high temperature corrosion and the formation of scaled heating surface, furnace slag, etc. It is very important to measure the gaseous metal concentration in the burning flame for the safety operation of high base coal and biomass boiler; meanwhile, it is important to guide the research of the reliving mechanism and model setting of alkali metal.
The fiber optic spectrometer taking CCD array as the spectral measurement component can detect the spectral radiation information of the burning flame under different wavelengths. It can be known from National Institute of Standards and Technology (NIST) Atomic Spectra Database that the characteristic atomic emission spectrum of main alkali metal is: Li (670.776 nm, 670.791 nm), Na (588.995 nm, 589.592 nm), K (766.490 nm, 769.896 nm) and Rb (780.027 nm, 794.760 nm), all of which favors the qualitative and quantitative analysis of alkali metal. The traditional alkali metal detection method is offline detection, such as flame atomic absorption spectrometry, flame photometry, inductive coupling inductively coupled plasma atomic emission spectrometry, graphite furnace atomic absorption spectrometry, etc.; the methods need to carry out pre-treatment to the collected sample to achieve the test condition. It has complex operation; the offline detection method cannot obtain the gaseous alkali metal distribution rule in the burning process. Along the development of laser technology, the researcher can measure alkali metal Na, K contents of brown coal and pine wood by Laser-Induced Breakdown Spectroscopy (LIBS). However, with regard to large industrial furnace, LIBS online detection technology has obvious disadvantages such as complex equipment, complex operation and high cost. Although LIBS detection neglects the temperature change, the constant temperature must be maintained, and the measuring conditions are rigorous, which is unfavorable to the industrial generalization of LIBS.